As Abbey suggested not being immediately apparent suggests noise sources elsewhere could dominate the noise floor.Just for the record, I pulled the master of my Venue today and found in the left summing amp position a NE5532 and in the right position a TL072. Didn´t notice it for a decade....
Weird. The fader being located after, it shouldn't have any effect there.Very, very slightly for example +6.93VDC with fader pulled down becomes +6.89V or so. The largest swing is on pin7 --- IC 1:
fader all the way up -1.309V, mid position -1.316V and pulled all the way down -1.296V.
Specifications:What is the bandwidth of your scope ? And sampling rate if digital.
Why don't you try the LME49720? It is available in PDIP, and the performance has nothing to envy to the 1656.At this point I'm convinced that OPA1612 hotter than I like operation is due to parts small size and heat dissipation mistreated on my part . I will install heat sinks on all 1612s and give them a chance. To my ears, they sound light years ahead of 072-5532 combo.
I did. It sounds better than 5532 IMO but still not as good as 1612, also 1656 is very good prefer it to 49720, but to my ears 1612 is a king. It has sound on its own. It adds depth and detail without being clinical and avoids that mid range "hole" that many other opamps have. I'm aware that all this is subjective and not everyone's preference.Why don't you try the LME49720? It is available in PDIP, and the performance has nothing to envy to the 1656.
Don't forget at the same time it reduces the OLG of the first opamp, so the overall stability is more or less intact.Going back to the original schematic, although one half (the 'B' section of the VE amplifier has a 75 Ohm resistor for 'isolation' (good), if you hang a long wire onto the insert send you start to curtail the HF negative feedback that goes back to the bus in the 'A' section of that chip. I suppose having the feedback invertor hanging from after the 75 Ohm resistor probably makes the situation worse.